1. Field of the Invention
The present invention relates to an electrophotographic method and an electrophotographic apparatus each using a charging unit of a corona discharge type. More particularly, the invention relates to an electrophotographic method and an electrophotographic apparatus each using an amorphous silicon based photosensitive member (hereinafter referred to as an a-Si photosensitive member) and, especially, to an electrophotographic method and an electrophotographic apparatus each capable of reducing ghost memory latent in the a-Si photosensitive member and relieving potential unevenness thereon, thereby providing image copies with high quality.
2. Related Background Art
In electrophotography, photoconductive materials making a photosensitive layer in the photosensitive member are required to have such characteristics as high sensitivity, high SN ratios [photocurrent (Ip)/dark current (Id)], possession of an absorption spectrum fit for spectral characteristics of radiated electromagnetic waves, quick optical response, possession of a desired dark resistance, being harmless to human bodies during use, and so on. Particularly, in the case of the photosensitive members for image forming apparatus built in the image forming apparatus used as business machines at offices, the nonpolluting property during the aforementioned use is a significant point. Hydrogenated amorphous silicon (hereinafter referred to as xe2x80x9ca-Si:Hxe2x80x9d) is a photoconductive material exhibiting an excellent property in this respect and, for example, Japanese Patent Publication No. 60-35059 describes application thereof to the photosensitive member for image forming apparatus.
The photosensitive members for image forming apparatus using a-Si:H are normally constructed by heating an electroconductive support at 50xc2x0 C. to 400xc2x0 C. and forming a photoconductive layer of a-Si on the support by a film forming method such as a sputtering method, an ion plating method, a thermal CVD method, a photo-CVD method, a plasma CVD method, or the like. Among these the plasma CVD method, which is a method of decomposing source gas by dc or high frequency or microwave glow discharge to form an a-Si deposited film on the support, is used as a preferred method in practice.
Japanese Patent Application Laid-Open No. 56-83746 suggests the photosensitive member for image forming apparatus consisting of an electroconductive support and a photoconductive layer of a-Si containing halogen as a constitutive element (hereinafter referred to as xe2x80x9ca-Si:Xxe2x80x9d). This Application describes that when a-Si contains 1 to 40 atomic % of halogen, it becomes feasible to provide the photoconductive layer of the photosensitive member for image forming apparatus with high heat resistance and good electrical and optical characteristics.
Japanese Patent Application Laid-Open No. 57-115556 describes the following technology for improvement in the electrical, optical, and photoconductive characteristics such as dark resistance, photosensitivity, optical response, etc. of the photoconductive member having the photoconductive layer made of the a-Si deposited film, in the operating environment characteristics such as humidity resistance or the like of the photoconductive member, and in stability with a lapse of time; a surface layer made of a nonphotoconductive amorphous material containing silicon and carbon is laid on the photoconductive layer made of an amorphous material comprising silicon as a matrix.
Further, Japanese Patent Application Laid-Open No. 60-67951 describes the technology about the photosensitive member comprising a deposited film of a transparent insulating overcoat layer containing amorphous silicon, carbon, oxygen, and fluorine, and Japanese Patent Application Laid-Open No. 62-168161 describes the technology using an amorphous material containing constitutive elements of silicon, carbon, and 41 to 70 atomic % of hydrogen, as a surface layer.
Further, Japanese Patent Application Laid-Open No. 57-158650 describes that the photosensitive member for image forming apparatus with high sensitivity and high resistance is made by applying to the photoconductive layer a-Si:H containing 10 to 40 atomic % of hydrogen and having a ratio of absorption coefficients of absorption peaks at 2100 cmxe2x88x921 and at 2000 cmxe2x88x921 in an infrared absorption spectrum in the range of 0.2 to 1.7.
On the other hand, Japanese Patent Application Laid-Open No. 60-95551 discloses the technology for improvement in the image quality of the a-Si photosensitive member, in which the image forming steps including charging, exposure, development, and transfer are carried out while the temperature near the surface of the photosensitive member is maintained at 30 to 40xc2x0 C., thereby preventing decrease of surface resistance due to adsorption of water on the surface of the photosensitive member and, in turn, preventing image run caused thereby.
These technologies improved the electrical, optical, and photoconductive characteristics and the operating environment characteristics of the photosensitive members for image forming apparatus and also improved the image quality in conjunction therewith.
With tendencies toward multiple utility of the electrophotographic apparatus and toward space saving at the offices and the like, there have been increasing desires for apparatus being effective to space saving and having multiple functions and fast copy speeds so as to meet the tendencies. Under such circumstances, increase in copy speed, reduction in size, and provision of multiple functions have to be sought from the design aspect.
However, the increase in copy speed, the reduction in size, and the provision of functions of the electrophotographic apparatus lead to reduction in size of the charging unit and increase in the process speed, so as to shorten a passing time of the photosensitive member in the charging unit, which makes it difficult to establish a high charge on the surface of the photosensitive member. From the aspect of energy saving, it is also necessary to lower power consumption of the entire electrophotographic apparatus by cutting the power to the drum heater and decreasing the value of electric current to the charging unit.
Particularly, with increase in the copy speed or with decrease in the diameter of the photosensitive member, there arises a significant problem about charging. In the case of the increase in the copy speed, even if the width of the charging unit is constant, the passing time of the photosensitive member in the charging unit becomes shorter, so as to result in degradation of chargeability. In the case of the decrease in the diameter, the width of the charging unit is limited, so as to fail to gain a sufficient charge.
A common problem to the increase of the speed and the decrease of the diameter of the photosensitive member is decrease of the time from exposure to the charging unit. In use of amorphous silicon, there arises a problem of optical memory due to exposure. This optical memory decreases with a lapse of time after exposure. Thus, the shorter this time, the easier a ghost appears in the image. In order to eliminate this optical memory called a ghost, it is possible to apply an excess amount of decharging (or charge-eliminating) exposure. However, degradation of chargeability resulted with increase in the amount of decharging exposure.
Japanese Patent Application Laid-Open No. 60-16187 discloses the technology for preventing the ghost by exposure with a decharging light of 600-800 nm, using a laser of near infrared exposure. Japanese Patent Application Laid-Open No. 58-102970 discloses the technology of preventing deterioration and improving the mechanical and chemical durability, using the wavelengths of 600 to 700 nm for the laser exposure.
There was, however, no publication disclosing a method of totally improving the chargeability, the ghost, the potential unevenness, etc. and thus the foregoing problems had to be solved for application to high-speed digital machines and digital machines with the compact photosensitive member of a-Si.
For designing the image forming apparatus and the electrophotographic image forming method, therefore, it is necessary to implement the improvement from the total viewpoint in the electrophotographic characteristics, the mechanical durability, etc. of the photosensitive member for image forming apparatus and accomplish further improvement in the charging apparatus with high charging efficiency and even charging and in the image forming apparatus, so as to solve the foregoing problems.
It is, therefore, an object of the present invention to provide an electrophotographic method and an electrophotographic apparatus that solve the prior art problems to the chargeability, the ghost, the potential unevenness, etc. and is suitable for application to high-speed digital machines and digital machines with the compact photosensitive member of a-Si.
It is another object of the present invention to provide an electrophotographic method and an electrophotographic apparatus that totally improve the electrophotographic characteristics, the mechanical durability, etc. of the photosensitive member for image forming apparatus and accomplish further improvement in the charging apparatus with high charging efficiency and uniform (or even) charging and in the image forming apparatus, so as to solve the foregoing problems.
According to a first aspect of the present invention, there is provided an electrophotographic method comprising forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material; a latent image is formed by the exposing with a light; the light has such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential; and the decharging is implemented by use of a light having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm.
According to a second aspect of the present invention, there is provided an electrophotographic method comprising forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material; a latent image is formed by the exposing with a light; and the light has such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential and has a full width at half maximum of a peak in the emission spectrum of not more than 50 nm.
According to a third aspect of the present invention, there is provided an electrophotographic method comprising forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material; a latent image is formed by the exposing with a light; the light has such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential and has a full width at half maximum of a peak in an emission spectrum of not more than 50 nm; and the decharging is implemented by use of a light having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm.
According to a fourth aspect of the present invention, there is provided an electrophotographic apparatus for forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material; an exposure for forming a latent image is implemented by use of a light having such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential; and the decharging is implemented by use of a light having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm.
According to a fifth aspect of the present invention, there is provided an electrophotographic apparatus for forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material, and an exposure for forming a latent image is implemented by use of a light having such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential and having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm.
According to a sixth aspect of the present invention, there is provided an electrophotographic apparatus for forming a toner image at least through decharging of a photosensitive member as a recording element, charging, exposing, developing, and transferring, wherein at least a light-receiving layer of the photosensitive member is comprised of an amorphous material; an exposure for forming a latent image is implemented by use of a light having such a peak wavelength in an emission spectrum as to make minimum a value of optical memory at a unit contrast potential and having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm; and the decharging is implemented by use of a light having a full width at half maximum of a peak in an emission spectrum of not more than 50 nm.